The Advantages and Disadvantages of Specific Mass Spectrometry Platforms

It’s well acknowledged that each mass analyzer (and ionization source) has unique performance attributes and limitations. The type of configuration, whether it is an ESI-quadrupole or a MALDI-TOF for example, is largely dictated by the flavor of research and the molecules of interest – and sometimes by the instrument or resources available. Regardless, it is important to know what the capabilities of each instrument are to see whether it is right (or at least adaptable) for your research needs. If not, it’s probably time to upgrade components or instruments. Here are a few specifications:

Quadrupole

Typical mass range – 3000 m/z

Typical resolution – 2000 – the observed m/z divided by the Δm/z for two ions that can be separated

Tolerance for high pressure – atmospheric

Well-suited for electrospray

Ease of switching between positive and negative ions

Small size

Relatively low cost

Mass range limited to about 3000 m/z

Poor adaptability to MALDI

Ion trap

Range 2000 m/z

Resolution 1500

Small size

Medium resolution

Simple design – Low cost

Well suited for tandem MS

Easy for positive/negative ions

Limited mass range – not as much a problem with current innovations

Time-of-Flight

Range m/z ∞

Resolution 350

Highest mass range

Very fast scan speed

Simple design – Low cost

Ease of adaption to MALDI

Low resolution

Difficulty of adaption to electrospray

Time-of-Flight reflectron

Range m/z ∞

Resolution 1500

Improved resolution relative to TOF

Very fast scan speed

Simple design – Low cost

Resolving power has limited m/z range

Lower sensitivity compared to TOF

Fourier transform

Range m/z ∞

Resolution 30,000

High resolution

Well-suited for tandem MS

High vacuum required

Super conducting magnet required – expensive

Extensive maintenance

Massive size

As you can see, the differences between these instrument platforms is significant in terms of capabilities, limitations, adaptability, requirements, and size. Each type has a specific set of skills that allow it to excel in certain applications.

One important point is that often times preferred performance and functionality can be conditional on limitations which may not significantly impact your analysis.

Furthermore, the instrument may have focused use in an area in which targets have been both defined and yet to be defined. Such a scenario might involve small molecule quantitation and discovery using a ESI Triple Quadripole in a clinical lab or one studying secondary metabolites in bacteria.

One step further, an instrument can be applied in a purely discovery oriented role where the source of the sample is defined, such as human blood, saliva, or cerebral spinal fluid, but the nature of the analyte is unknown.